Milton a



Oct. 26 1926.

M- A. FESLER SAFETY DEVICE FOR BURNERS v origina Filed June 19. 192s 2 santa-sunt@ v Alz'lta/z A. @6751' MVM clumsy@ Oct. 26', 1926. Re. 16,444

M. A. FEsLER SAFETY` DEVICE FOR BURNERS original Filed June 19. v1925 2 Shoots-Shu'.

' 10 andantu M7121 laf/f Gttormu's mei-.ien

. from becoming overheat sectionalview throuh a furnace 'showing t Reime@ oa. ze, 192s.

UNITED STATESJ Rye. i

PATENT OFFICE.

MILTON A. msnm, or armonia, coNNEc'rIcU'r, assIsNon, BY misma assicuruEN'rs, 'ro coHBUsrIoN-coN'rnoL conrona'rIoN, oFnos'roN, massacnvsn'r'rs. a.

CORPORATION 0F DELAWARE.

sarn'rY-nnvrcr: ron sonrisas.

v original no.' 1,514,728, ama February as, 192s, serial no. 35,213, mea :im is, 192s. imputation :er

reissue led July 12, 192B. Serial No. 128,909.

v V'This invention relates to a safety control thermostat for burners for stopping the sup- -ply of fuel upon failure of the fuel to lgmte- In theruse of oil burners in furnaces it .is extremely important that means be pro- 'vided for automatically cutting 011:' the supsly of fuel to the burner incase the fuel ischar ed from the burner is not ignited, for if t e fuel is not consumed as it is deliveredby the burner it will accumulate in Y or about the furnace in a highly inflammable condition.- l y It has been proposed heretofore to use a thermostat for cutting -oi the sup ly o f fuel to a burneru n-failure of the el to ignite, but diiicu ty..fhas been experienced in developing a thermostat control that will operate promptly, due to .the fact that if the thermostat is placed sutliciently` close to the burner to operate roniptl when the burner is started it is-ligelyto e injured by the h eat o the kfurnace when the latter .has reached its normal operating`temperatux-e,

and if the thermostat is located-inthe furnace stack, or insome position remote from the burnerfit will not o perate promptly.

One important feature of the invention therefore resides in a safety control thermostat that is located' near the burner where it will be uickly heated, and in the conor p'reventin he thermostat Anot r feature of the invention resides lin the' onstruction for stopping the 'su ply of fuel tothe burner upon failure o the `fuel issuingV fr'onithe burner toignite. Other features of the invention and novel combination of parts in addition .to 'the above will be hereinafter in connection with the accompanying' drawings..

which illustrate one good practicalform of the invention.

. In the drawings,- Fig. 1 is a-horizontal, the front portion of e burnerfin its opera'l tive position and showin the electrical connections diagrammatical y.

Fig. 2" is a front elevation of the parts shown in Fig. 1, the burner bein cut by a vertical transverse sectir`and t e cover plate of the switch. being removed; and

Fig. 3 is a vertical sectional view taken on line 3 3 of Fig. 2. Y

The safety control thermostat of the present' invention may be used in connection A with either domestic or commercial ful' nac-es, but it is particularly well adaptedj for use in domestic furnaces of the intermittent firing type such as are controlled by automatic means which frequently stop and start the burner.

In the embodiment of the invention illustrated, it is assumed that the burner 10is 4of the tl ethat' employsa blast of air to atomizc i A e oil, and air is, supplied to the burner by a fan which is driven by the electric motor'12 It is further vassumed that to the nare read for combustion, and stopping the e `76,

' an o ening 13 formed in the'refractory materia 14 which is vmounted within the metal frame 15. L PThe material `14 may be secured within the frame 15 bythe set screw 16, and air cell insulating material 17 may be providedv between lthe inner face of the frame 1'5 and the refractory material 14.

the motor 12 drives an pil pump or oper- The frame 15 is provided with aA frontwardly extending annular flange 18 that surrounds the burner 10, and an atomizer 19 at the discharge end of the burner serves to direct the atomized-fuel outwardly, indicated by the lines a.

A gas or other form of pilotis provi/ded to the' burner to be changes,

vgf

to ignite the fuel as it is discharged Ifrom the burne1',"and the pilot is shown' as comprising the gas vpipe 20, the inner end of which extendsinwardly through an opening 21 in the refractory material.

`As stated, an important feature ofthe present invention resides in a safety control thermostat which is located suiiiciently close quickly heated thereby, and 'which is protected from the-intense'heatlof the burner. In the construction shown a thermostatic element 22 is mounted in an opening 23 formed in the refractory material 14 at one side of the burner where it will be J tween the front face of the vcasing and the inner -faceof the flange plate 26. Since thethermostatic element 22 is lmounted within Aa relatively deep hole in the furnace wall, it is well protected from the destructive action of the high temperature of the burner, while at the Sametime it is` in position to 'be quickly, heated bythe burner.l The hole 23 forms a :passage through whichfcurrents of air may venter the 'furnace about the thermostatic elementl to reduce its temperaturel and these currents l ofair are automatically controlled by the' expansionaid contraction of the element 22 as will presentlyfappear. 4 AWhen airis .permitted to How into the furnace through the hole 23 it will not onl element 22, but it-wi l also drive back the heat' of the `burnerto'p'revent lit from entering the o ening 23, Vthus effectually rotecting the t lerm'ostatlc' eleme temperatureof 'thefurnacef Withintheh'ub 25 is rotatably mountedv theshaft 30,r the inner end of whlchextends" inwardlythrough the coiled thermostatic element 22,"andthe collar 31 is rigidly secured to theinner end of the shaft in the desired hand direction,

position f 'adjustment by' a Vsetv screw32,"

while the innerend ofthe coiled strilp` secured to'thiscollarby a screw 33. ing sleeve 34 ri 22 is bearft from moving in the hubin a right viewingFig.-3, and a collar 36 which -is secured to the shaft 30 by apin 37 abuts against the opposite end of the hub and prevents the shaft therein in a lefthand direction. The construction ofthe' thermostatic coil 22 is such that as the' temperature ofthe same4 increases the casing cool the thermostatic 'idly secured yto theshaft 30 l laag ascrew orms a stop to preventthe from moving.

clockwise direction, and 'as its temperature decreases it will contract and rotate the shaft in a contra-clockwise direction.

Rotation of the sha-ft 30 by the thermostatic element 22 serves to open and close an electric switch. -Various means to this end might be provided, and in the construction shown the electric switch and means for operating the same are mounted in the casin 38 which is rigidly securedto the hub 25 an the front face of the vcasing 38 is closed by late 3 9 which may be secured to the casing y'screws 40.

The casing 38, as shown, extends upwardly from the supporting hub 25 and lares'outwardly in an Jupward direction to provide suiiicient room in the upper portion of the to accommodate the switch to be described. In the construction shown a mercury switch is pivotally supported by the bolt 42,the inner end of which is screwed into a plug 43 extending inwardly from the inner face of the casing. The 'me ury switch may comprise a glassiube 44 t la posite ends of which are received-in cupshaped supporting elements 45 which are secured to th'e opposite ends of the block 41, and a conductor wireor the like '46, extends from screw 47 at one end 0f the block into one end of the tube 44, while a second conj ductor wire 48 dips into a mercury cu 49 formed at the lower wall of tube 44, an'dpthis conductor 48 isconnected to the other contact screw 47. -Th'e construction of the mercury switch 'is such that when' it is tilted about' its pivot 41 to the\fposit ion shown in Fig. 2 the mercury will flow towards one end of the tube away from the mercury which is imprisonedin thecup portion 49, lthus breakingthe circuit, and when the tube .is tilted in the op osite direction, the mercury at the left han the bottom of the tube to close the circuit.-

The contact screw 47 at the right hand' end of the tube is connected tov a terminal screw 50 .by the wire 51 and the contact end thereof will flow .along A screw-47 at theleft hand end ofl thetube i vis 'connected to a secondterminal .screw 52 by the wire 53. i'

In the construction rocking movement is/ imparted to themercury sv'vithV fronithe shafty 30 by an' operating arm 54. It is desirable that tl1e'arm54 be frictionally Secured to the shaft 30 so that the swinging movement imparted `to the arm 54 may be restricted withoutrestrict'ing the turning movement of the shaft 30, the arm 54is provided'w'itli and to this end a hub 55 which `rotatably receives theshaft 30 and this hubisb provided with pins 56 which project slida y ably mounted on the shaft30, the inner face of which Vcollar rests a inst the sleevex36 which is rigidly secure to the-shaft.

into holes formed in a collar'5'7 rotatsleeve 57 and a.

coiled sprin 58 confined between the ace of the lever 54 serves i to hold the sleeve 57 in frictional enga ement with the collar` 36 and the friction etween these elements may be varied as desired by adjusting the nut 59 which retains lthe arm 5 4 in place uponfthe operating shaft.

The upper end of the armA 54 is provided witha laterally extendingrpin 60-which engages a' slot formed in the downwardly extending portion of the metal strip 61 that Yin is secured to the block 41 by the screw 62, the arrangement being such that as the arm 54 rocks it will rock the block 41 and meri cury switch about the shaft 42. The rockmovement imparted to thc mercury switch may be limited by adjusting `the stop screws 63 adjustably mounted in the upper wall of the casing 38. Y v

It will be noted that the lever arm 54 '1s very much longer than the lever arm 61 and that therefore a very small angular movement of the shaft will produc/e the angular movement of block 41 to open or close the circuit controlled by the mercury switch.

` This. is important, as will be made to ap- Since the thermostatic element 22 is lo.`

cated near the burner where it will be quickly heated,it `is neceary toprovide means :to prevent the same from berng injured by the high'tem rature 'of thejburnerand this uis accomplis ed, `in vaccordance 'with lthe prezentinvention, by providing means for regulatin the flow ofcooling currents of air into t eJ furnaceabout the thermostatic element.- Various means-to this end might be provided, and, `in the construction shown,

it is laccomplishedrby. forming a number of holes -64 vin the `flange plate 26 for the passageof air into the furnace through the hole 23 to coolv off the thermostatic element 221 It is desirable that this .J cooling air shallpass through theopening 23 only when the thermostatxc element is heated and that the openings 64 be closed when the burner isinactive so that the element 22 willbequick- `ly` heated as soon as the. burner is started.

To thislend the flange plate 26 is provided with a shutter orV cover 65 comprisingadisk which lis provided with the annular flange portionl 66 that is journalled on the fixed hub 25. The shutter 65 is provided with the openings 67 positioned to be aligned with" the openings 64i Qupon turning the shutter, 'andin order that the shuter 65 may be rotated Yby the shaft 30 a coll'r 6 8 mounted upon this shaft is rigidly secured thereto b a bolt 69, the outer end of which extends trough a slot 70 formed in the annular.

flange 66v to rotate with the shutter.

As a result of the construction just described, Ythe element 22 upon becoming heated will turncthe shutter 65 to admit, air

through the aligned openings 64 and 67so that air will be drawn into the furnace through theseopenings to cool ofi' the element 22, and the movement of the shutter will be in proportion to the expansion of the element* 22 under different temperature.V 1t will therefore be seen that rela-tively' slight changesl i'n the temperatureof the thermostatic element will move the shutter to vary the amount of cooling air admitted to the element 22 and this will tend to keep the thermostatic element at a temperature much below the high temperaturel of the furnace. `-\Vhen 'the fire goes out, the air enterin the furnace about the elementJ 22 Vwill qulckly cool `this element, whereupon it will rotate the'shutter 65 tothe closedl position to remain in this-fposition until'the furnace is a ain heated. This is desirable because if t e shutter is closed when the burnerv is lighted the thermostatic element will be quickly heated sufficiently to voperate the electric switchy It win be noted thaatecausebf theuifz ference in lengths of the lever arms 54 andl 61, the mercury switch `will be quickly shifted at the beginning of the retum movement of the shaft 30 due to cooling resulting from,y

absence of fire and that this movement wilt take place before there is any great return movement of the shutter. That is 'to say;

the 'opening 23 is 'kept -open long after the switch has been shifted to cause a stoppage' of fuel delivery so that the thermostatlc elel ment cannot be reheated to throw the switch to operative position as a result of heat re.

tained in the furnace after there has been a failure of combustion. Y .j A' J The mercury switch above described which fis controlled by the thermostatic' `element 22 may be employed i'n various ways to stop the supply of fuel .to the" burner when Vthe atomizedffuel discharged by the burner is notignited by the ilot or in case the fire goes out. One desira le form of wiring circuit to the end is shown in Fig. 1, wherein' it is assumed that T desi ates a thermometer controlled switch o well known con.- struction' and which is adapted to be mounted in a room of a house to start the oil burner Y when the temperature of the-room falls belowa predetermined point, and t stop the burner when the temperature of the room rises above this. point.

operated from the usual electric light circuit o a house using. alternating current, and the operation of the motor 12 is controlled by the switch 71v which is connected to one conductor of the usual electric lig t :systemby the wire'72 and is connected to t e other conductor of the electric light systemv by wire 73. The switch 71 is shown as 1n its open position and is adapted to be moved in the right hand direction to close the switch The motor 12 whichcontrols the operation of the burner may be the -l and start the motorA whereby Athe wire 72 -willbe connected to the wire 74 leading to one terminal of the motor andthe wire 73 will be connected to the wire 75 leading to the other terminal of the motor. f

In order that the switch T may be siiiiciently sensitive to maintain the temperature of a room at substantially a constant temperature and may make and break the 19 circuit without-sparking, it is desirable that 4the current supplied tothis switch be of much lower voltage than. that commonly eni- 'llcliyed in the ordinary electric light circuit.

e switch T is therefore not directly con- `nected to the electric lighty circuit, but is connected to a seconda-ry circuit supplied with current produced by -the`transformer consisting of the primary coil 76., andthe Secondary coil 77. The primary coil 76 is connected across the current supply wires 72 and 73. One terminalof the secondarv coil 77 is connected to the contactv pin 78 of the switch T by the wire 79, and the opposite terminal of the secondaryA coil 77 is connected to the switch closing coil 80.V The oppowith a second vcontact, pin84wh1chcooper-l atesI with the contact pm 78 to prevent oscil- 4 the contuctor 81 ofl the holding c'oil 8O byl i Y forty seconds 95 switch 44.

site terminal of' the coil 80 is connected by the conductor 81 to the switch ,Y 82 which serves to complete the-circuit between the` 3'0- coil 80 and' the wire 83 when the main switch 71 is moved to Lthe motor operating ition. The wire 83 leads to' one termina of .the switch T.

The switch T, which, as stated, is ofnwell known construction, is commonl provided 4lation or repeated flashng'on and oil' of the circuit when the same isc being made -or broken. This contact pin 84 is connected to the wire 85, the aran ement being such that the current from the 84 engage their cooperating elements, whereupon the switch 82 is closed to insure the .main switch being lheld in its closed` position.

until the temperature of the thermometer switch T has dropped suciently to openy th circuit of thecontacts 78 and 84.

From thewiring circuit so far described it willbe seen that the temperature con-AA open and close the` .the burner, but,'

trolled switch T serves to switch 71 to start and sto 'as above pointed out, it 1s important that means be provided for'lpromptly cutting olf the supplyV of fuel tc t ev burner 1Q in case .the fuel dischargedtherefrom' is'not ignited by thepilot 20. To' `this'endis provided a. delay switch vwhich is aranged to st motor 12 at the end cfa short interval of time, say -if the thermostatic element 22A is not heated during that short'period--of time by the 'burner to5actuate the mercury periodv of time,

secondary coil 77 willnot pass through the holding coil 80 to close the main switch until both contacts 78 and rents of air.

,.This--isvaccomplished in the wiring arrangement shown in Fig. 1 by a second transformerqhaving a I'prima terminal of which 1s connecte to the motor operating wire by the wire 87A and the 4other` terminalV of which vis connected to the motor operating wire 74 by the wire 88.`

`c0il 86, one

withthe delayheating coil 9 1 is a switch 94 which is `normally closed, and `which is f included in so that if this switch is penedit will-im mediatelv cut olf the supplyof current to the holding coil 80 and cause the -Inain switch 71' to open and stop the motor 12.

The mercury switch 44, as above Stated, is

.closed when the thermostatic element 22" is not heated, so that as soon as the main switch y71 is 4closed to start the motor 12, current is supplied' to "the delay heating coil 91 and the .same-graduallyheats a strip of thermostatic metal 95 which, at theend of a short in'a direction to open the switch` 94, should the mercury switch 44 fail to be opened and cutoff the current to the heating element 9 1 prior to this occurrence.

the circuit 79 above ,mentionedI say forty seconds, Awill lex' From the foregoing it will be understood tioned near the'burner whereit'` will "be that the thermostatic element 22- is pOSiquickly heated upon starting the burner so l that it will act promptly to open the mercury switch .to prevent the motor from being lsto ped by the. delay heating element 91,

an it will also be understood that as the temperature of the element '22 increases it' l will open'the shutter to admit coolingcur Should, for. any reason, the fuel dischargled by the burner 10 fail tobe ignited' by t e e mercury yswitch, and at the end of a short period of time,' say` forty seconds, the delay eating element 94 will eii'ect the opening of e pilot, thenthe thermostatic ment 22 'will not be heated to openthethe switch 91 to 'stop the motor. The switch 94 will not operate unless the fuel discharged by theburner fails to ignite, and when once open, the parts have cooled' off l and the same is it will remain openuntilV manually closed by. the reset button 96,' 'i

after the burner defecthas been corrected.

Since the operating arm 54 is frictionall secured to the shaft 30 and moves throug cury switch, afslight movement of the shaft 30 in either direction will serve to tlirov'v` the switch, while the friction connection be only a short distance to actuate theme12 i said ' 'control to the 46 Y thermostatic 'surrounds the element'and forms an air 65 air passage,

further movement to be imparted' to the shaft to actuate the shutter.

' What is claimed is Y 1. In combination with a burner, a safetyy control thermostat, comprising in'- combination, a thermostati element mounted near theburner .to be quickly 'heated thereby, means controlled by said element'for cutting oi the supply of f uel tothe burner, a sha rotatably supported :adjacent said element and mechanically connected to the free endof the element to berotated by its contraction and expansion, means controlled by the 1I thermostatic element for cutting oil lthe supply of fuel to the burner, and means actuated by the turning of said shaft to control the iow of cooling currents of-air tothe thermostaticI element for preventing its ,S0 overheating.

2. In combination with a furnace burner,

' :athermostatic element mounted near the tween the shaft and am win -f permit Vburner o burner to be quickly heated thereby, a shaft.

s mounted to be rotated by the expansion and 1, 26 contraction of ,said element, an electric switch o rable by the movement of said L shaft an adapted to control the supply of' fuel to the burner, and a shutter mounted to shaft and adapted to control the supply era'ting mechanism and controlled by the t ermostatic element to be actuated upon failure of the fuel to ignite, and means controlled by the thermostatic element to regulate the flow of air into the furnace through said passage to' cool the element.

5. In combination with a furnace, a burner' for the furnace, a thermostatic element mounted in an opening in a'wall of the furnace in position to be quickly heated. a shaft adapted to be rotated bychan es in the temfperature of said element, a hu for rotatably supporting said shaft, means for supporting the hub at said opening in spaced relation to the walls thereof,'means actuated by the rotation of said shaft to control the passing of cooling currents of air through the opening about the thermostaticqelement, and means actuated by shuttin oft' thesupply of fuel to theburner when t e fuel fails to ignite.

6. In combination with a furnace, a burner for the furnace, a thermostatic element supported in position to be heated quickly by the burner, a shaft adapted to be rotated by changes in trolling the passage of coolingv currents of be 'opened and closed by the movement of of fuel to the burner, and a shutter mounted v tobe opened and closed by the movement'of said shaft4 to admit cooling air to the 'element. 3. In combination with a burner, a safety burner yto be quickly heated thereby 40 in a fixed position while its other end is free to rotate under temperature changes, a

air to said element to prevent it from over heating, aswitch actuated by said shaft, and

electric means controlled by said vswitch forv mounted' near the burner in position to be quickly heated and arranged to be cooled'by shutter for controlling the iow of air about `the thermostatic element to cool the same and connected to the free end of j the element to be rotated to the n position as the temperature vof the rmostatic element increases and to the closed position as the temwrature drops, and means controlled by sai element to cut i of the sup ly of fuel to the burner when the fuel f s to 4. In combination with a burner, a safety control thermostat, comprising in combination a'thermostatic element mounted in posio tion to be heated by the burner and vprovided with a thick protecting wallo'r housing that sage through which air may entei' the .constructedto .extend inwasrg? toward. the interior of the furnace a x cient `distance to exclude Yfrom the thermostatic element practically cept those that enter the inner endof the means associated with the 3?" nace vabout the element, said wall or housingv 6- being all heat rays excurrents of air entering the furnace, means the rotation of sald shaft for a safetyi vcontrol thermostat, a thermostatic element thermostat mounted suiiiciently close alsl theftemperature of said element, lmeans actuated by the shaft for concontrolled by said element to cut off the supplyof fuel tothe burner when the fuel fails toignite, flow of cooling currents -of air past the and a shutter for controlling the thermostatic element'and mechanically -con- -nected to the element so that it is opened different amounts in proportion to the expansion and contraction of the element to' vary the volume of'vair throughout ajsubstantial 8 In vc ombination with a burner, ty control thermostat, comprising in comblnation, a thermostatic element mounted near the burner in position Ato be quickl heated and provided with .a surrounding w All forming an air passa leading into the furnace lefby said element to cut off means control the supply of fuel to the burner when the fuel fails'to ignite and a shutter for con trolling the flow of cooling currents of air into the furnacethrou h said passage and mechanically connecte -to the thermostatic element sothat it is -opened different amounts in proportion to 'the temperaturev changes to increase the air volume in proportion to the increase in the temperature in said element.' -s

l 9. In combination. with a burner, a safety .control thermostat, comprising in combination, a thermostatic element mounted inl po -si-tion to be heatedby the burner and'arranged to 'be cooled by currents of air enter- Y ing the furnace, means controlled by sai l element to cut olf the supply of fuel to the' burner when the fuel fails to ignite, and adjustable means for controlling the flow of' tion o the'thermostatic elementfto vary the Y volume" of air throughout a 'substantial range.

10. In combination with a burner, a safety control thermostat,comprisin in combinationa thermostatic element mountedl in positidn to be heated by the burner and pro-y .vided with a protect' wall that surrounds the element in spaced re ation thereto to form an air passage ending into the furnace, said wall being constructed to form a vhousing about the elementthat extends toward the interior ofthe furnace beyond the element to exclude practically a'll heat rays from the -thermostatic element except Jthose that enter the inner end of said assage, means coni 30 trolled by `the thermostatic element to cutoff the supply of yfuel to the. burnerwheii the fuel fails to ignite, and'. mechanically controlled means actuated by y element to regulate the' flow of lair through Vl said passage about the element.I v

11. In combination with a furnace 'having a thick wall of refractory material, a burner having its discharge end projectinginto the l furnace through saidvwall, a the'rmostatic 40 element mounted near. the burner tobe heatedtherebyandfpositioned in a passage.

formed throughfthe thick furnace wall and in aced relation to the walls of the passage to shecooled b' airfcurrents enterin .45 furnace throug said passage, the wa s of the paage being formed the interior of the furnace be ond the thermostatic element to .protect it ly-allheat raysexcept those that -enter 'the inner ,end of thepassage, means controlled by the thermostatic element to cut of the supply of fuel tothe burner when the fuel fails to ignite, and adjustable means for controlli'n the ow of cooling current of air through til controlled by the expansion and contraction of said element.

" 12. In' combination with control thermostatz comprising in, combina- 00 tion, a thermostatic element mounted near the -burner and positionedl in a pass formed'in a wall of the furnace so that it'is protected by the .walls of the passa from all heat rays except those that'enter tig .05 endof the passage and is subject lto the cooling action of air currentsentering the furnacethrough said passage, means controlled d one o -structed so that its surrounding walls enclose kenter` the inner end the air currents passing the"I tliermostatic thel to project toward' rom practical-` e lpassage about said elementfand` a-burner, a safety' inner by said element for cutting off the supply of `fuel to the burner, and a closure 'for the outer end of said passage amdadjustable -to position to cut oif the How of airt erethrou h that"said element may be quickly lheate and adjustable to a second position to permit air to pass .throughthe passage and drive'jbaclr the heat, andmechanical means controlled by the expansion and contraction of saidelement to actuate the closure.

13. In combination with a` furnace having a burner, a safety control thermostat comprising in combination, athermostati elel'ment mounted in en opening formed in a wall of the furnace near the burner` so that it is cooled byv air passingvintthe furnace through the opening, said ening being conand protect the thermostatic element from practically all heat ra except those that e ope'i'ii'n'r and cause through e opening to\drivel the heat of the lburner back away from the mouth'of the` opening, means cony trolledy by the thermostaticrelement to -cut olf the su ply of fuel to the burner whenl the fuel ails to ignite, and mechanical] controlled lmeans actuated by` the theimostatic element to control the ilow`of air through said opening about said element. 14.v A heating unit comprising a fuel burner. a fuel director by means of whichrlow of4 fuel to the burner 4may be maintained or discontinued, a thermostat arrangedto be responsive to conditions in the combustion' zonevv of the burner, a circuit switch actuated by said thermostat, an electricv circuit .coui-J prisin said circuit switchrand means for' contro ng the-fuel director, and means ac` tuated by the thermostatfb which the ther-i' mostat may beprotected from the vheat of combustion subsequent to -a shifting of the sw'itch in one diretion and-'the protection maintained untilafter the switch has been reversed by cooling of the therm0stat. v

15. A heating unit comprising a fuel burnn er, a fuel director bymeans of which flow of fuel to the burner may be maintained or discontinued, a thermostat arranged within the direct influence of acombustion zone of the,` burner, 'a circuit switch actuated by said thermostat, an electric circuit comprising said 'circuit' switch and means 'for controllin the fuel director, and meansfby which a coo ing current' of air may be direetedupon said thermostat, said means comprising a shutter controlled by the thermostat. and opened subsequent.v to .the actuation of the switch due to cinbustionfzzonel heatandlclosed subsequent to-actuation of the switch due to lack of combustion zone'heat. j .g

16. heating unit comprising a fuel burner, a fuelA r by means of which ow' 130 of fuel to the burner maybe maintained or discontinued, a controller for said director, a thermostat arranged within the direct influence of the combustion zone of the burner and comprising a movable element, a memberl actuated b said movable element and connected to t e Controller to fully shift it upon initial movement of the movable element of the thermostat in either direction, a shutter arranged to control flow of cooling currents of air adjacent the thermostat, and a connection between said shutter and the movable element of the thermostat.

` MILTON A. FESLER. 

